Comment 29 for bug 36158

ACPI is complicated and a lot of people seemingly get it wrong.

Back in the late 90s ACPI was very new and an awful lot of BIOS vendors were creating BIOSes that did awful things to the hardware when ACPI was turned on. I used a K6-III that had random lockups with ACPI turned on. However over time ACPI became a little bit more reliable (there are still a sad number of cases of BIOSes being released with bad ACPI though).

Anyway so many of the old BIOSes had broken ACPI it was decided that an arbitrary cut off date *for the BIOS itself* should be set. BIOSes with ACPI that were older than this date would need ACPI to be forced in order to use it. This avoided having to create a blacklist for each individual old BIOS (remember if an update comes out it is seen as different and if it were broken it might have to be listed seperately) with broken ACPI out there.

Most people never run into this because their BIOS is new enough that ACPI defaults to on however there are cases of people with pre 1999 BIOSes that don't have broken ACPI but do have broken APM.

You can see a Red Hat dev talking about the Ubuntu BIOS cut off year here:
http://kernelslacker.livejournal.com/30664.html

I suppose the question is was the patch that Ubuntu was carrying to disable the cutoff dropped on purpose?